well-goknown/vendor/github.com/decred/dcrd/dcrec/secp256k1/v4/nonce.go

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// Copyright (c) 2013-2014 The btcsuite developers
// Copyright (c) 2015-2020 The Decred developers
// Use of this source code is governed by an ISC
// license that can be found in the LICENSE file.
package secp256k1
import (
"bytes"
"crypto/sha256"
"hash"
)
// References:
// [GECC]: Guide to Elliptic Curve Cryptography (Hankerson, Menezes, Vanstone)
//
// [ISO/IEC 8825-1]: Information technology — ASN.1 encoding rules:
// Specification of Basic Encoding Rules (BER), Canonical Encoding Rules
// (CER) and Distinguished Encoding Rules (DER)
//
// [SEC1]: Elliptic Curve Cryptography (May 31, 2009, Version 2.0)
// https://www.secg.org/sec1-v2.pdf
var (
// singleZero is used during RFC6979 nonce generation. It is provided
// here to avoid the need to create it multiple times.
singleZero = []byte{0x00}
// zeroInitializer is used during RFC6979 nonce generation. It is provided
// here to avoid the need to create it multiple times.
zeroInitializer = bytes.Repeat([]byte{0x00}, sha256.BlockSize)
// singleOne is used during RFC6979 nonce generation. It is provided
// here to avoid the need to create it multiple times.
singleOne = []byte{0x01}
// oneInitializer is used during RFC6979 nonce generation. It is provided
// here to avoid the need to create it multiple times.
oneInitializer = bytes.Repeat([]byte{0x01}, sha256.Size)
)
// hmacsha256 implements a resettable version of HMAC-SHA256.
type hmacsha256 struct {
inner, outer hash.Hash
ipad, opad [sha256.BlockSize]byte
}
// Write adds data to the running hash.
func (h *hmacsha256) Write(p []byte) {
h.inner.Write(p)
}
// initKey initializes the HMAC-SHA256 instance to the provided key.
func (h *hmacsha256) initKey(key []byte) {
// Hash the key if it is too large.
if len(key) > sha256.BlockSize {
h.outer.Write(key)
key = h.outer.Sum(nil)
}
copy(h.ipad[:], key)
copy(h.opad[:], key)
for i := range h.ipad {
h.ipad[i] ^= 0x36
}
for i := range h.opad {
h.opad[i] ^= 0x5c
}
h.inner.Write(h.ipad[:])
}
// ResetKey resets the HMAC-SHA256 to its initial state and then initializes it
// with the provided key. It is equivalent to creating a new instance with the
// provided key without allocating more memory.
func (h *hmacsha256) ResetKey(key []byte) {
h.inner.Reset()
h.outer.Reset()
copy(h.ipad[:], zeroInitializer)
copy(h.opad[:], zeroInitializer)
h.initKey(key)
}
// Resets the HMAC-SHA256 to its initial state using the current key.
func (h *hmacsha256) Reset() {
h.inner.Reset()
h.inner.Write(h.ipad[:])
}
// Sum returns the hash of the written data.
func (h *hmacsha256) Sum() []byte {
h.outer.Reset()
h.outer.Write(h.opad[:])
h.outer.Write(h.inner.Sum(nil))
return h.outer.Sum(nil)
}
// newHMACSHA256 returns a new HMAC-SHA256 hasher using the provided key.
func newHMACSHA256(key []byte) *hmacsha256 {
h := new(hmacsha256)
h.inner = sha256.New()
h.outer = sha256.New()
h.initKey(key)
return h
}
// NonceRFC6979 generates a nonce deterministically according to RFC 6979 using
// HMAC-SHA256 for the hashing function. It takes a 32-byte hash as an input
// and returns a 32-byte nonce to be used for deterministic signing. The extra
// and version arguments are optional, but allow additional data to be added to
// the input of the HMAC. When provided, the extra data must be 32-bytes and
// version must be 16 bytes or they will be ignored.
//
// Finally, the extraIterations parameter provides a method to produce a stream
// of deterministic nonces to ensure the signing code is able to produce a nonce
// that results in a valid signature in the extremely unlikely event the
// original nonce produced results in an invalid signature (e.g. R == 0).
// Signing code should start with 0 and increment it if necessary.
func NonceRFC6979(privKey []byte, hash []byte, extra []byte, version []byte, extraIterations uint32) *ModNScalar {
// Input to HMAC is the 32-byte private key and the 32-byte hash. In
// addition, it may include the optional 32-byte extra data and 16-byte
// version. Create a fixed-size array to avoid extra allocs and slice it
// properly.
const (
privKeyLen = 32
hashLen = 32
extraLen = 32
versionLen = 16
)
var keyBuf [privKeyLen + hashLen + extraLen + versionLen]byte
// Truncate rightmost bytes of private key and hash if they are too long and
// leave left padding of zeros when they're too short.
if len(privKey) > privKeyLen {
privKey = privKey[:privKeyLen]
}
if len(hash) > hashLen {
hash = hash[:hashLen]
}
offset := privKeyLen - len(privKey) // Zero left padding if needed.
offset += copy(keyBuf[offset:], privKey)
offset += hashLen - len(hash) // Zero left padding if needed.
offset += copy(keyBuf[offset:], hash)
if len(extra) == extraLen {
offset += copy(keyBuf[offset:], extra)
if len(version) == versionLen {
offset += copy(keyBuf[offset:], version)
}
} else if len(version) == versionLen {
// When the version was specified, but not the extra data, leave the
// extra data portion all zero.
offset += privKeyLen
offset += copy(keyBuf[offset:], version)
}
key := keyBuf[:offset]
// Step B.
//
// V = 0x01 0x01 0x01 ... 0x01 such that the length of V, in bits, is
// equal to 8*ceil(hashLen/8).
//
// Note that since the hash length is a multiple of 8 for the chosen hash
// function in this optimized implementation, the result is just the hash
// length, so avoid the extra calculations. Also, since it isn't modified,
// start with a global value.
v := oneInitializer
// Step C (Go zeroes all allocated memory).
//
// K = 0x00 0x00 0x00 ... 0x00 such that the length of K, in bits, is
// equal to 8*ceil(hashLen/8).
//
// As above, since the hash length is a multiple of 8 for the chosen hash
// function in this optimized implementation, the result is just the hash
// length, so avoid the extra calculations.
k := zeroInitializer[:hashLen]
// Step D.
//
// K = HMAC_K(V || 0x00 || int2octets(x) || bits2octets(h1))
//
// Note that key is the "int2octets(x) || bits2octets(h1)" portion along
// with potential additional data as described by section 3.6 of the RFC.
hasher := newHMACSHA256(k)
hasher.Write(oneInitializer)
hasher.Write(singleZero[:])
hasher.Write(key)
k = hasher.Sum()
// Step E.
//
// V = HMAC_K(V)
hasher.ResetKey(k)
hasher.Write(v)
v = hasher.Sum()
// Step F.
//
// K = HMAC_K(V || 0x01 || int2octets(x) || bits2octets(h1))
//
// Note that key is the "int2octets(x) || bits2octets(h1)" portion along
// with potential additional data as described by section 3.6 of the RFC.
hasher.Reset()
hasher.Write(v)
hasher.Write(singleOne[:])
hasher.Write(key[:])
k = hasher.Sum()
// Step G.
//
// V = HMAC_K(V)
hasher.ResetKey(k)
hasher.Write(v)
v = hasher.Sum()
// Step H.
//
// Repeat until the value is nonzero and less than the curve order.
var generated uint32
for {
// Step H1 and H2.
//
// Set T to the empty sequence. The length of T (in bits) is denoted
// tlen; thus, at that point, tlen = 0.
//
// While tlen < qlen, do the following:
// V = HMAC_K(V)
// T = T || V
//
// Note that because the hash function output is the same length as the
// private key in this optimized implementation, there is no need to
// loop or create an intermediate T.
hasher.Reset()
hasher.Write(v)
v = hasher.Sum()
// Step H3.
//
// k = bits2int(T)
// If k is within the range [1,q-1], return it.
//
// Otherwise, compute:
// K = HMAC_K(V || 0x00)
// V = HMAC_K(V)
var secret ModNScalar
overflow := secret.SetByteSlice(v)
if !overflow && !secret.IsZero() {
generated++
if generated > extraIterations {
return &secret
}
}
// K = HMAC_K(V || 0x00)
hasher.Reset()
hasher.Write(v)
hasher.Write(singleZero[:])
k = hasher.Sum()
// V = HMAC_K(V)
hasher.ResetKey(k)
hasher.Write(v)
v = hasher.Sum()
}
}